From Bulbapedia, the community-driven Pokémon encyclopedia.
The Trick Master in the anime
The Trick Master (Japanese: カラクリ大王 King of Tricks) is a character in the Ruby, Sapphire, Emerald, Omega Ruby, and Alpha Sapphire. He lives on Route 110 in the Trick House.
He provides the player with eight challenges (six challenges in Omega Ruby and Alpha Sapphire), each beginning with him hiding somewhere in the front room. Once the player finds him, he gives a small speech and says that he will be hiding in the back. Once the player completes the challenge, he will reward them with a prize.
After all challenges are completed, the Trick Master disappears, leaving behind only a note saying he has gone to distant lands to search for new tricks.
In the anime
He makes his anime appearance in A Poké-BLOCK Party!, though he is referred to as The King of Tricks in the dub.
Every year he holds a contest at his Trick House. Whoever could get through his Trick House first would win a one-year supply of Pokéblocks. Many believe he is a strange character.
In the Pokémon Adventures manga
The Trick Master is a close friend of Wattson and Emerald and helped them design their gadgets. Although he originally appeared as a minor character in the Ruby & Sapphire chapter, he redesigned the electric mecha hidden inside New Mauville so it could fly and helped Sapphire return to the ruins of Sootopolis City and participate in the final battle by heavily recharging Minun and Plusle. It's also revealed that he likes to visit different places other than Hoenn to improve his designs.
He makes his only other appearance beside the two in Emerald's flashback towards the end of the sixth chapter. He is revealed to have helped Emerald, recommending him to Earl Dervish's Pokémon academy and building his outfit and equipment.